Atmospheric turbulence resistant open-air optical communication system

ABSTRACT

An open-air optical communication system is provided which enhances accuracy and reliability of signal transmission by utilizing multiple optical receivers. Two or more receivers are positioned within the path of a collimated optical beam emitted by a remote transmitter. The receiving lenses are of equal size and are positioned apart in a plane perpendicular to the optical beam a distance at least as great as the receiving lens diameter. The receiving lenses thereby receive two or more signals through different optical paths. All of these signals are electronically combined to yield one composite received signal that is better than any one of the individual received signals. The system employs automated gain control circuitry to further eliminate any signal fluctuations caused by atmospheric phenomena such as turbulence, fog, smoke, dust, rain, snow, etc. By utilizing multiple receivers, degradation of the transmitted signal due to atmospheric turbulence induced optical scintillation is significantly reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an open-air optical communicationsystem that avoids signal degradation due to attenuation and scattering.

2. Description of the Prior Art

Open-air optical communication systems have been available for decadesand cover the range from single RS-232 units operating at 1200 bps tohigh-speed ATM units capable of live video broadcasts. While allconventional optical communication systems operate with weather relatedconstraints, continuing advances in bandwidth improvement, costreductions, and the minimization of atmospheric affects have aided inbringing optical communication systems into the mainstream ofcommunication products available to the telecommunications engineer.Exemplary developments in this regard are reported in the followingrecent technical papers: T. Wang, G. R. Ochs, and S. F. Clifford, ASaturation-resistant Optical Scintillometer to Measure C_(n) ² , J. Opt.Soc. Am. 68, 334 (1978); S. F. Clifford, G. R. Ochs, and R. S. Lawrence,“Saturation of Optical Scintillation by Strong Turbulence”, J. Opt. Soc.Am. 64, 148 (1974); R. S. Lawrence, G. R. Ochs, and S. F. Clifford,“Measurements of Atmospheric Turbulence Relevant to OpticalPropagation”, J. Opt. Soc. Am. 60, 826 (1970); G. R. Ochs, and Ting-I.Wang, “Finite Aperture Optical Scintillometer for Profiling Wind andC_(n) ² ”, Appl. Opt., vol. 17, No. 23, 3774-3778 (1978); R. M.Gagliardi and S. Karp, Optical Communications, John Wiley & Sons, Inc.,New York, 1995; C. P. Primmerman, et. al., “Atmospheric-CompensationExperiments in Strong-Scintillation Conditions”, Applied Optics 34, No.12, p. 2081-2088, 1995; and J. H. Shapiro, “Imaging and OpticalCommunications Through Atmospheric Turbulence”, Laser Beam Propagationin the Atmosphere, J. W. Strohbehn, Ed., Springer-Verlag, New York,p.171-222, 1978.

Despite significant advances in the field of open-air opticalcommunication, the development of such systems has been hampered bycertain basic, underlying effects upon open-air optical communicationsystems that are unique to this type of communication. Specifically, theatmospheric optical channel may be seen as clear air, or it may containparticles from dust, fog, mist, or precipitation. When a light beampasses through the atmosphere containing fog, rain, or other particles,both attenuation and scattering occur. A collimated beam broadens due tothe scattering, thus resulting in losses in signal strength. Duringheavy fog or snow, the light beam is totally obscured. Under suchconditions no light can be transmitted to the other end of thecommunication system so that the open-air communication channel isinterrupted. Essentially, there is no simple solution to overcome thebasic limitations imposed by the laws of physics.

However, even in clean air conditions, atmospheric turbulence-inducedoptical scintillation may severely affect the quality of opticalcommunications systems. Atmospheric turbulence induced opticalscintillation is particularly important to understand when designingwireless communication solutions using an optical device. The shimmeringeddies seen above a hot surface and the twinkling of stars are examplesof turbulence induced optical scintillation. Temperature gradientswithin and between these eddies cause refractive index changes on thelight as it passes from a transmitter to a receiver through theseeddies. These changes act as additional optical lenses that orient andrefocus the optical beam. Most of the light intensity fluxuation thatoccurs is a result of the refraction of the beam of light. That is, itresults from scattering rather than attenuation.

SUMMARY OF THE INVENTION

Despite certain basic limitations, open-air optical communicationsystems do have some very significant advantages. Specifically they donot require any buried or overhead cable systems, which are extremelyexpensive to construct and which present considerable maintenancedifficulties. Also, open-air optical communication systems arerelatively insensitive to electrical disturbances from sources such aslightning, transmission in proximity to power lines, and fluxuations insolar radiation. Moreover, the components employed in open-air opticalcommunication systems are typically quite reliable. Therefore, open-airoptical communication systems do present considerable advantages,particularly if the problems arising from optical scintillation can besolved.

The present invention provides one of the most important and costeffective solutions to the minimization or even elimination of opticalscintillation problems. This invention largely obviates the problem ofoptical scintillation by utilizing a “multiple optical receiver” design.A system constructed according to the invention integrates two or morereceivers to overcome fading or scattering conditions that may be causedby optical scintillation or beam wandering induced by atmosphericturbulence. The multiple receiver design actually receives two or moresignals through different optical paths from the same opticaltransmitter. All of these signals are combined to yield one compositereceived signal that is better than any of the individual signals.

For the open-air optical communication system of the present inventionto be most effective, each optical receiving lens employed in thereceiving unit should be spaced from any other receiving lens in thatunit by a distance at least equal to the diameter of the lens in a planeoriented perpendicular to the collimated optical beam received. Thisconfiguration ensures that all received signals are subject toindependent scintillating effects. By processing signals that are notsubject to the same scintillating effect, significantly improvedperformance is achieved. Also, an automated gain control (AGC) circuitryis employed to further eliminate any signal fluxuations caused byatmospheric phenomena such a turbulence, fog, smoke, dust, rain, snow,etc.

For a total of n channels there are a corresponding number ofindependently received, incoming optical signals. That is, for nchannels the system produces the following corresponding signals: S₁, S₂. . . S_(n).

In the automatic gain control circuitry, these signals are combined.That is, the combined signal S results from combining all of thereceived signals together (S=S₁+S₂+ . . . S_(n)).

In any open-air optical communication system, there must be a minimumdetection threshold for a signal in order for the system to have asatisfactory performance. This minimum threshold may be indicated by theterm S_(th). For any signal S_(i) (i=1, 2, . . . n)<S_(th) the systemwill fail.

If the probability that each signal S_(i)<S_(th) is p, then theprobability for the combined signal S<S_(th) is p^(n).

This mathematical relationship provides a huge advantage for thecombined signal to have a satisfactory performance. For example, if foreach individual channel the failing probability p=10⁻³, a single channelsystem will not provide a satisfactory performance one out of a thousandtimes. Using a dual receiver system according to the present invention,on the other hand, the probability of failure is reduced to 10⁻⁶. Thatis, the system will fail only one time in a million. The improvement isa factor of one thousand. If more than a pair of receiving lenses andphotodetectors are employed, the improvement is even more significant.

In the foregoing calculations it is assumed that all received signalsare passing through independent paths. To ensure this independence ofthe atmospheric turbulence induced optical scintillations, theseparation of the receiving lenses must be at least larger than thediameter of the lens.

In one broad aspect the present invention may be considered to be anatmospheric turbulence resistant optical communication system. Thissystem is comprised of a transmitter and a receiver. The transmitterincludes a waveform shaping modulator, an optical source, and beamforming optics for producing a collimated optical beam. A laser diode isan excellent choice as the optical source of an open-air opticalcommunication system for its ease of light collimation and modulation.The receiver is located in a line-of-sight path with the optical beamand includes a plural number of focusing receiving lenses of equaldiameter spaced apart in a plane normal to the optical beam a distancegreater than the receiving lens diameter. The receiver also includes aseparate photodetector for each of the receiving lenses, as well asseparate, signal controlled gain amplifiers for each of thephotodetectors. The receiver further employs an automatic gain controlcircuit coupled to receive and combine inputs from all of the signalcontrolled gain amplifiers and conditioned to provide a combined outputsignal of constant level.

In another broad aspect the invention may be considered to be anopen-air optical communication system that minimizes distortion due toatmospheric attenuation and scattering. The optical communication systemof the invention is comprised of an optical transmitter that generates acollimated optical beam from a modulated light source. It also includesan optical receiver including a plurality of receiving lenses of equaldiameter and equal focal lengths all located in optical communicationwith the optical transmitter and in the path of the optical beam. Theselenses are separated from each other in a direction perpendicular to theoptical beam by a distance at least as great as the receiving lensdiameter. The receiver includes a separate optical photodetectorproducing an electronic output for each of the receiving lenses. Aseparate signal controlled gain amplifier circuit is coupled to each ofthe optical photodetectors for detecting the signal-to-noise ratio ofelectronic output therefrom. An automated gain control stage receivesinputs from all of the signal controlled gain amplifier circuits. Theautomated gain control stage produces a combined electronic outputsignal weighted in accordance with the signal-to-noise ratios of thesignal controlled gain amplifier circuits.

In still another broad aspect the invention may be considered to be animprovement of an open-air optical communication system employing atransmitter that generates a collimated optical beam modulated by acommunication signal and a receiver disposed in the optical path of thecollimated optical signal beam to detect and to modulate the collimatedoptical beam to extract the communication signal therefrom. According tothe improvement of the invention the receiver is comprised of aplurality of receiving lenses of equal diameter. All of these lenses liein the optical path of the collimated optical beam and are separatedfrom each other in a plane normal to the optical path by a distance atleast as great as the receiving lens diameter. A separate photodetectorfor each of the receiving lenses is provided to independently detect thecollimated optical beam therethrough. Separate gain amplifiers areprovided for each of the photodetectors. A common, automated gaincontrol circuit is coupled to receive inputs from all of the separategain amplifiers and to combine the inputs to produce a singledemodulated output communication signal having a constant level.

The optical communication system of the invention provides a transparentcommunication solution for short distance DS-1 and E1 applications. Theunique technology designed into this system integrates opticaltransceivers into a wireless transmission media that yields a very costeffective solution for line-of-sight distances up to one kilometer. Thesystem also provides license-free operation and is quite transportable,since each transceiver weighs only 1.5 kilograms. The system provides ahigh fade margin, dual receive architecture, and plug-and-playinstallation. The fade margin is twenty decibels.

The optical communication system of the present invention may be usedwith private networks, competitive access providers, and local exchangenetworks. Its uses include teleconferencing, voice, data, and videocommunications. It may be utilized for primary and redundant links. Itmay also be employed as a last mile connection and in surveillancemonitoring. The optical communication system of the invention may beused as a temporary communication system, since it is capable of rapiddeployment. This makes it especially useful in disaster recoverycircumstances.

The invention may be described with greater clarity and particularity byreference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one transceiver in a full duplexopen-air optical communication system constructed according to theinvention. The transceiver of FIG. 1 is shown without its protectivecover to permit the internal components thereof to be more clearlyillustrated.

FIG. 2 is a perspective view illustrating an optical communicationsystem according to the invention which employs a pair of atmosphericturbulence resistant open-air optical communication transceiversaccording to FIG. 1.

FIG. 3 is a block diagram of one of the optical transmitters employed inthe system of FIG. 2.

FIG. 4 is a block diagram of one of the optical receivers employed inthe system of FIG. 2.

FIG. 5 is a schematic diagram of the waveform shaping circuitry employedin the transmitter depicted in FIG. 3.

FIG. 6 is a schematic diagram of the laser diode driving circuit and thelaser diode employed in the transmitter of FIG. 3.

FIG. 7a is a schematic diagram of one of the photodetectors and itspreamplification circuitry employed in the receiver of FIG. 4.

FIG. 7b is a schematic diagram of the other photodetector and itspreamplification circuitry employed in the receiver of FIG. 4.

FIG. 8a is a schematic diagram of the signal controlled gain amplifierfor the photodetector and preamplifier of FIG. 7a.

FIG. 8b is a schematic diagram of the signal controlled gain amplifierfor the photodetector and preamplifier circuitry of FIG. 7b.

FIG. 9 is a schematic diagram of the automated gain control circuit ofthe invention employed in the receiver of FIG. 4.

DESCRIPTION OF THE EMBODIMENT

As illustrated in FIG. 2, a full duplex open-air optical communicationsystem according to the invention may be constructed utilizing a pair ofoptical transceiver units 10 and 12. The transceivers 10 and 12 areidentical in all respects and are positioned in optical combination totransmit and receive signals to and from each other. The electronic andoptical components of the transceivers 10 and 12 are each housed withina weather-resistant case 16 having a cover 18 seated thereon in aweather-tight fashion. FIG. 1 illustrates one of the opticaltransceivers 10 or 12 with the cover 18 removed therefrom.

The physical dimensions of the case 16 of each of the transceivers 10and 12 is one hundred millimeters in height, one hundred eightymillimeters in width, and two hundred ninety millimeters in depth. Thesystem employs a 12-volt DC nominal power supply and may be operatedbetween 0° C. to 50° C. Each of the transceivers 10 and 12 weighs 1.5kg.

As illustrated in FIG. 1, each transceiver 10 and 12 is provided with atransmitter, indicated generally at 20. The transmitter 20 is alaser-type GaAlAs having a laser wavelength of 780-940 nanometers. Thebeam divergence is 0.5 to five mrad with an average power of five toforty milliwatts. The optical aperture is twenty-five millimeters. Theelectronic components of the transmitter 20 are mounted upon a printedcircuit board 22. The transmitter 20 includes a waveform shapingmodulator 24, an optical source which is preferably a laser diode LD1,and laser diode driver circuitry indicated generally at 28 in FIG. 3.The beam forming optics of the transmitter 20 include a convex, one-inchdiameter beam forming transmitting lens 40. The collimating lens 40 isfocused on the laser diode LD1 and produces a collimated optical beamindicated generally at 42 in FIGS. 2 and 3.

The transceivers 10 and 12 are each designed with a dual opticalreceiver 30 that enhances system performance. This dual receiver systemprovides both data redundancy and path diversity to minimize the effectsof turbulence. Both of the signals received by the receiver 30 arecompared with each other and the best signal is weighted in the combinedoutput to ensure optimal performance.

Installing and aligning the transceivers 10 and 12 is quite simple. Allthat is required is to mount the transceivers, align them, and connectthem to a power source and a DSX-1 or E1 source. The only special toolneeded is a visual alignment scope 14 which is included with each of thetransceivers 10 and 12.

The optical transmitters 20 of the transceivers 10 and 12 are identicalto each other. Only one transmitter 20 is illustrated diagrammaticallyin FIG. 3 and schematically in FIG. 5. Each optical transmitter 20 isformed of three elements, namely the waveform shaping modulating circuit24, the optical source, which is the laser diode LD1 and its laser diodedriver circuitry 28, and beam forming optics, namely the convextransmitting lens 40.

Optical communication systems require a light source that can be easilymodulated. Open-air optical communication systems must have a means toinject information signals, that is data, on the light source to projectit to a distant receiver. Focusing of the modulated light isaccomplished with beam forming optics. Ideally, the lens 40 collectslight from a point source, namely the laser diode LD1, and expands it toa perfect parallel beam. In practice, however, the beam 42 expandsduring propagation to a size that is a function of the diameter of thetransmitting lens 40, the focal length of the transmitting lens 40, anddistance from the laser source LD1 to the lens 40. Typical divergencefor optical communication systems are on the order of severalmilliradians.

In FIG. 2 the transceiver 12 is illustrated as being operated in thetransmitting mode to produce the collimated optical beam 42, and thetransceiver 10 is illustrated as being operated in the receiving mode.As shown in that drawing figure, the single transmitting lens 40 of thetransceiver 12 emits a collimated beam 42 that has an elliptical crosssection with a vertically oriented major axis indicated at 44.

In the embodiment depicted, each of the transceivers 10 and 12 isequipped with a receiver 30 that employs only a pair of receiver lenses32 and 34 of equal size, preferably about two inches in diameter. Asillustrated in FIG. 2, the receiver 30 of the transceiver 10 is locatedin a line-of-sight path with the optical beam 42. The focusing receivinglenses 32 and 34 are spaced apart in a horizontal direction along theminor, horizontal axis 46 of the collimated beam 42, in a plane normalor perpendicular to the optical beam 42.

Each lens 32 and 34 is provided with a separate photodetector which ispreferably a direct detection or noncoherent receiver such as a pinphotodetector. Preferably each receiver 30 employs two silicon pinphotodiodes U10 and U17 having a field of view of three to fifteen mradsand an optical aperture of fifty-four mm. The lenses 32 and 34 focus thereceived beam 42 onto their photodetectors U10 and U17, respectively.The receiving lenses 32 and 34 are spaced apart from each other adistance greater than their diameter along the horizontal, minor axis 46of the elliptical cross section of the collimated beam 42. Asillustrated diagrammatically in FIG. 4, separate signal controlled gainamplifiers 36 and 38 are provided for the photodetectors U10 and U17.

Each receiver 30 also includes an automatic gain control circuit 50coupled to receive and combine inputs from all the signal controlledgain amplifiers 36 and 38. The automatic gain control circuit 50 isconditioned to provide a combined output signal of constant levelderived from the electronic output signals of the photodetectors U10 andU17 responsive to their optical inputs from their respective receivinglenses 32 and 34. Preferably, the receiver 30 further includes opticalfilters 52 located in front of each of the receiving lenses 32 and 34 toreduce the effects of background radiation. These filters are indicateddiagrammatically in FIG. 4.

Although the effects of scattering and attenuation may improve byincreasing the number of receiving lenses, with each lens having its ownphotodetector and signal controlled gain amplifier, an increase in thenumber of lenses does increase the cost of the device. Therefore, in theembodiment illustrated only two receiving lenses 32 and 34 are employed.However, it is to be understood that any number of additional lenseswith their dedicated photodetectors and signal controlled gainamplification circuits can be utilized in accordance with the invention.

With reference to FIG. 4, the signal controlled gain amplifiers 36 and38 detect the signal-to-noise ratio from their respective photodetectorsU10 and U17. The automatic gain control circuit 50 provides the combinedoutput with a contribution from each photodetector U10 or U17 weightedin accordance with its signal-to-noise ratio.

As indicated in FIG. 3, the input signal waveform is shaped by awaveform shaping stage 24 to restore the waveform which may bedeteriorated by the input line 60. The reshaped waveform then modulatesa laser diode driver 28 with output power control to safely drive thelaser diode LD1. The center, small lens 40 of each of the transceivers10 and 12 is the transmitting collimator. The laser diode LD1 is placedat the focal point of the lens 40 to form a collimated beam projected toa distant receiver 30 in the other of the two transceivers 10 and 12depicted in FIG. 2. The two larger lenses 32 and 34 focus differentportions of the incoming beam 42 upon the separate photodetectors U10and U17.

A waveform shaping circuit 54 is also employed in demodulating theoutput of the automated gain control circuit 50 in the receiver 30. FIG.5 depicts circuitry that includes both the transmitting waveform shapingcircuit 24 and the receiving waveform shaping circuit 54. As illustratedin FIG. 5, the transmitter input line signal 60, which may have beendeteriorated, passes from a jumper block 62 through a transformer T2 topins 14 and 15 of an IC analog, T1 PCM Repeater/Transceiver chip U1. Thereshaped waveform of the input signal on line 60 is provided as anoutput from the IC chip U1 through pins 9 and 10 on lines 64 and 66,respectively. This signal is then passed through a differentialamplifier U2. From the output 68 of the differential amplifier U2 thesignal is passed to the laser diode driver circuitry LD1, illustratedschematically in FIG. 6.

The other half of the T1 PCM Repeater/Transceiver chip U1 is used as thewaveform shaping circuit 54 for the optical receiver 30. The receivedsignal from the automatic gain control stage 50 is provided on line 70as an input to pins 1 and 2 of chip U1. The reshaped waveform appears asan output on lines 72 and 74 at pins 6 and 7 of chip U1. The receivedsignal then passes through output transformer T1 to the end user. Whenthe transceivers 10 and 12 operate in the receive mode, the receivedsignal output from the chip U1 also appears as a line output on line 60.

The optical communication system of the invention may be utilized forshort distance DS-1 and E1 applications. For a DS-1 application, chip U1is a model LXT312 and the crystal oscillator X1 generates a 6.176 MHzfrequency signal. For E1 users the chip U1 is a model LXT313 and crystaloscillator X1 generates an 8.129 MHz frequency signal.

The laser diode driver circuitry 28, indicated in FIG. 3, is illustratedschematically in FIG. 6. The reshaped signal from operational amplifierU2 in FIG. 5 that appears on line 68 is fed through transistors Q2 andQ3 in FIG. 6 to drive the laser diode LD1. Variable resisters VR2 andVR3 are used to adjust the DC bias of transistors Q2 and Q3respectively. The output laser power is monitored and is fed on line 76to pin 2 of the laser diode driver U7. Variable resister VR4 is used toadjust the laser output power to the design power.

The photodetectors U10 and U17 are respectively positioned at the focalpoints of receiving lenses 32 and 34. The two optical signals from thereceiving lenses 32 and 34 are detected, respectively, by the twophotodetectors U10 in FIG. 7a and U17 in FIG. 7b. Each received signalis amplified by two amplifier stages. The operational amplifiers U8 andU9 in FIG. 7a amplify the signal from photodetector U10 detected byreceiving lens 32. Similarly, the operational amplifiers U15 and U16amplify the signal from photodetector U17 detected by receiving lens 34.Once the outputs of the photodetectors U10 and U17 have beenpreamplified, they are provided as outputs 80 and 82, respectively,corresponding to the two channels of the receiver 30 that are employed.The outputs 80 and 82 are fed to the signal controlled gain amplifiers36 and 38 associated therewith. These amplifiers are schematicallyillustrated, respectively, in FIGS. 8a and 8 b.

In the signal controlled gain amplifier 36 the signal on line 80 isfirst amplified by an amplification stage operational amplifier U11.Similarly, the signal on line 82 in the signal controlled gain amplifier38 in FIG. 8b is amplified by an operational amplifier U18. The outputsignals 84 and 86 from operational amplifiers U11 and U18, respectively,are then passed through low-pass filters to amplifiers U12 and U19,respectively, to clean up noise on the signals.

The output signal level is also detected by two rectified stages in eachof the signal controlled gain amplifiers 36 and 38. Specifically,operational amplifiers U13 and U14 in FIG. 8a detect the output signallevel derived from the receiving lens 32, while operational amplifiersU20 and U21, shown in FIG. 8b, detect the signal level produced from thereceiving lens 34. These measured signal levels appear at 88 and 90,respectively.

The measured signal levels 88 and 90 are used to control the impedancebetween the source and drain of an associated field-effect transistor(FET). The signal level on line 88 controls the impedance between thesource and drain of field-effect transistor Q4 in FIG. 8a, while thesignal level on line 90 controls the impedance between the source anddrain of field-effect transistor Q5 in FIG. 8b. A stronger signal levelon lines 88 and 90 will induce a smaller impedance of the FET to whichit is connected to give a larger gain of its associated amplifier U11 inFIG. 8a and U18 in FIG. 8b. Therefore, a larger signal level will resultin a larger gain at the channel output 92 in FIG. 8a and the channeloutput 94 in FIG. 8b. These signals are combined with each other asinputs into the automated gain control circuit 50, showndiagrammatically in FIG. 4, and illustrated schematically in FIG. 9.

By weighting the gain of the amplifiers U11 and U18 in accordance withthe signal-to-noise ratio, the signal controlled gain amplifiers 36 and38 amplify outputs from their respective photodetectors U10 and U17 witha gain that is proportional to the signal-to-noise ratio thereof. As aresult, the combined output signal to the automated gain control circuit50 is weighted greatest by the photodetector U10 or U17 having thegreatest signal-to-noise ratio.

The two signals from lines 92 and 94 of FIGS. 8a and 8 b, respectively,are added in the automated gain control circuit 50, illustrated in FIG.9, through resistors R28 and R29. These inputs are fed into an amplifierstage operational amplifier U6. The output signal from amplifier U6 online 96 is passed through a low-pass filtering, operational amplifierU5, to clean up the noise. The output signal level on line 98 isdetected by two rectifier stages formed by operational amplifiers U3 andU4. The measured signal level is used to control the impedance betweenthe source and drain of a field-effect transistor Q1. A stronger signallevel will induce a smaller impedance of the field-effect transistor Q1to give a smaller gain of amplifier U6. This ensures that the outputsignal on line 98 is always a constant that is independent of the inputsignal level.

The level of the automatic gain control circuit output on line 98 can becontrolled by adjusting the variable resistor VR1 in FIG. 9. Theautomatic gain control circuit 50 will eliminate any signal fluctuationcaused by atmospheric effects such as turbulence, fog, smoke, dust,rain, snow, and so forth.

The values and designations of the preferred electronic circuitcomponents shown in the schematic drawings of FIGS. 5 through 9 are setforth in Table 1 at the end of this description of the embodiment.

The digital interface for the electronics shown in FIGS. 5 through 9 maybe for either DSX-1 or E1 applications. When employed for DSX-1 thesystem standard is a single DS-1 Bellcore TR-NWT-00499 having a linerate of 1.544 Mb/s and a line code of AMI or B8ZS. The line code isfield selectible. The system employs an RJ-48C connector with a standard100Ω balanced interface.

When employed in E-1 applications, the standard utilized is an ITU-T(CCITT G.703) having a line rate of 2.048 Mb/s and an HDB3 line code.The connector employed in this system is a BNC standard 75Ω unbalancedconnector.

Undoubtedly, numerous variations and modifications of the invention willbecome readily apparent to those familiar with optical communicationsystems. Accordingly, the scope of the invention should not be construedas limited to this specific embodiment depicted and described. Forexample, any plural number of receiving lenses with associatedphotodetectors and circuitry may be employed. The greater the number ofreceiving links, the greater the accuracy and the reliability of thesystem. Naturally, however, each additional receiving lens andassociated photodetector and circuitry increases the expense of thesystem.

TABLE 1 Ref. Manufacturer Des. Description Manufacturer Part Number C1CAP, ELECTROLYTIC, PANASONIC ECE-A1EGE101 RADIAL, 25 V, 100 UF, 20%, 0.1LS C2 CAP, ELECTROLYTIC, PANASONIC ECE-A1EGE101 RADIAL, 25 V, 100 UF,20%, 0.1 LS C3 CAP, ELECTROLYTIC, PANASONIC ECE-A1EGE101 RADIAL, 25 V,100 UF, 20%, 0.1 LS C4 CAP, POLY FILM, PANASONIC ECQ-V1H105JZ3 RADIAL,50 V, 1.0 UF, 5%, 0.2 LS, STACKED C5 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C6 CAP,ELECTROLYTIC, PANASONIC ECE-A1EGE101 RADIAL, 25 V, 100 UF, 20%, 0.1 LSC7 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C8 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED C9 CAP, MONOLITHIC MALLORY M15G479D2 CERAMIC,RADIAL, 200 V, 4.7 pF, 0.5% COG, 0.1 LS C10 CAP, CERAMIC, MURATARPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C11 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC12 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C13 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED C14 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C15 CAP, CERAMIC, MURATARPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C16 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC17 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C18 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED C19 CAP, CERAMIC, MURATA RPE110COG150J50VRADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C20 CAP, CERAMIC, MURATARPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C21 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC22 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C23 CAP, MONOLITHIC MURATA RPE110COG4R7J50V CERAMIC, RADIAL,ERIE 50 V, 5 PF, 5% COG, 0.1 LS C24 CAP, MONOLITHIC MURATARPE110COG470J50V CERAMIC, RADIAL, ERIE 50 V, 470 PF, 5% COG, 0.1 LS C25CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS,STACKED C26 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15 PF,ERIE 5% COG, 0.1 LS C27 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL,50 V, 0.1 UF, 5%, 0.2 LS, STACKED C28 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C29 CAP,MONOLITHIC MALLORY M15G229D2 CERAMIC, RADIAL, 200 V, 2.2 PF, 0.5% COG,0.1 LS C30 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF,5%, 0.2 LS, STACKED C31 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL,50 V, 0.1 UF, 5%, 0.2 LS, STACKED C32 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C33 CAP,ELECTROLYTIC, PANASONIC ECE-A1EGE101 RADIAL, 25 V, 100 UF, 20%, 0.1 LSC34 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22 UF, 20%,0.1 LS C35 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22UF, 20%, 0.1 LS C36 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50V, 22 UF, 20%, 0.1 LS C37 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220RADIAL, 50 V, 22 UF, 20%, 0.1 LS C38 CAP, CERAMIC, MURATARPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C39 CAP,CERAMIC, MALLORY M15G279D2 RADIAL, 200 V, 2.7 pF, 0.5% COG, 0.1 LS C40CAP, POLY FILM, PANASONIC ECQ-V1H103JZ RADIAL, 50 V, 0.01 UF, 5%, 0.2LS, STACKED C41 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15PF, ERIE 5% COG, 0.1 LS C42 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C43 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C44 CAP, CERAMIC,MALLORY M15G279D2 RADIAL, 200 V, 2.7 pF, 0.5% COG, 0.1 LS C45 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC46 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C47 CAP, MONOLITHIC MALLORY M15G229D2 CERAMIC, RADIAL, 200V, 2.2 pF, 0.5% COG, 0.1 LS C48 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C49 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C50 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC50 CAP, MONOLITHIC MURATA RPE110COG150J50V CERAMIC, RADIAL, ERIE 50 V,15 PF, 5% COG, 0.1 LS C51 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL,50 V, 0.1 UF, 5%, 0.2 LS, STACKED C52 CAP, MONOLITHIC MURATARPE110COG470J50V CERAMIC, RADIAL, ERIE 50 V, 470 PF, 5% COG, 0.1 LS C53CAP, MONOLITHIC MURATA RPE110COG4R7J50V CERAMIC, RADIAL, ERIE 50 V, 5PF, 5% COG, 0.1 LS C54 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50V, 15 PF, ERIE 5% COG, 0.1 LS C55 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C56 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C57 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC58 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C59 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15PF, ERIE 5% COG, 0.1 LS C60 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C61 CAP, CERAMIC, MURATARPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C62 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC63 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C64 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED C65 CAP, POLY FILM, PANASONIC ECQ-V1H104JZRADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C66 CAP, ELECTROLYTIC,PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22 UF, 20%, 0.1 LS C67 CAP,ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22 UF, 20%, 0.1 LSC68 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22 UF, 20%,0.1 LS C69 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50 V, 22UF, 20%, 0.1 LS C70 CAP, ELECTROLYTIC, PANASONIC ECE-A1HGE220 RADIAL, 50V, 22 UF, 20%, 0.1 LS C70 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL,50 V, 15 PF, ERIE 5% COG, 0.1 LS C71 CAP, CERAMIC, MALLORY M15G279D2RADIAL, 200 V, 2.7 pF, 0.5% COG, 0.1 LS C72 CAP, POLY FILM, PANASONICECQ-V1H103JZ RADIAL, 50 V, 0.01 UF, 5%, 0.2 LS, STACKED C73 CAP,CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1LS C74 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%,0.2 LS, STACKED C75 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V,0.1 UF, 5%, 0.2 LS, STACKED C76 CAP, CERAMIC, MALLORY M15G279D2 RADIAL,200 V, 2.7 pF, 0.5% COG, 0.1 LS C77 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C78 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC79 CAP, MONOLITHIC MALLORY M15G229D2 CERAMIC, RADIAL, 200 V, 2.2 pF,0.5% COG, 0.1 LS C80 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50V, 0.1 UF, 5%, 0.2 LS, STACKED C81 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C82 CAP, CERAMIC,MURATA RPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C83CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS,STACKED C84 CAP, MONOLITHIC MURATA RPE110C0G470J50V CERAMIC, RADIAL,ERIE 50 V, 470 PF, 5% COG, 0.1 LS C85 CAP, MONOLITHIC MURATARPE110COG4R7J50V CERAMIC, RADIAL, ERIE 50 V, 5 PF, 5% COG, 0.1 LS C86CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5% COG,0.1 LS C87 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF,5%, 0.2 LS, STACKED C88 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL,50 V, 0.1 UF, 5%, 0.2 LS, STACKED C89 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C90 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC91 CAP, CERAMIC, MURATA RPE110COG150J50V RADIAL, 50 V, 15 PF, ERIE 5%COG, 0.1 LS C92 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED C93 CAP, CERAMIC, MURATA RPE110COG150J50VRADIAL, 50 V, 15 PF, ERIE 5% COG, 0.1 LS C94 CAP, POLY FILM, PANASONICECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKED C95 CAP, POLYFILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2 LS, STACKEDC96 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1 UF, 5%, 0.2LS, STACKED C97 CAP, POLY FILM, PANASONIC ECQ-V1H104JZ RADIAL, 50 V, 0.1UF, 5%, 0.2 LS, STACKED CR1 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 CR2 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 CR3 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 CR4 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 CR5 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 CR6 SEMIC, DIODE, DIODES INC. 1N4148 HIGH SPEEDRECT., 100 PIV, DO-35 J1 CONN., RJ48C, CENT. AMP 5202514 LATCH, 8 POS.,W/PNL. STOPS, RA, PCB MT. J2 CONNECTOR, CUISTACK CP-2350 CIRCULAR, DIN,5 SOCKET, RA, PCB MT. J3 HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 LPOST, 2X36, GOLD J4 HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 L POST,2X36, GOLD J5 HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 L POST, 2X36,GOLD J6 HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 L POST, 2X36, GOLDJ7 HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 L POST, 2X36, GOLD J8HEADER STICK, SULLINS PZC36DAAN .025 SQ/.230 L POST, 2X36, GOLD LD1SEMIC, LASER SHARP LT022MC DIODE, 780 nm, P1 CONN, MULTIPIN BERG65043-033 MOLDED, DBL ROW, MINI LATCH HOUSING, 8 POS P2 CONN, MULTIPINBERG 65043-033 MOLDED, DBL ROW, MINI LATCH HOUSING, 8 POS P3 CONN,MULTIPIN BERG 65043-034 MOLDED, DBL ROW, MINI LATCH HOUSING, 6 POS P4CONN, MULTIPIN BERG 65043-034 MOLDED, DBL ROW, MINI LATCH HOUSING, 6 POSP5 CONN, MULTIPIN BERG 65043-033 MOLDED, DBL ROW, MINI LATCH HOUSING, 8POS P6 CONN, MULTIPIN BERG 65043-033 MOLDED, DBL ROW, MINI LATCHHOUSING, 8 POS Q1 SEMIC, TRANSISTOR, NATIONAL 2N5460 JFET, P-CHANNEL,TO-92 Q2 SEMIC, TRANSISTOR, 25C752 NPN, Q3 SEMIC, TRANSISTOR, 25C752NPN, Q4 SEMIC, TRANSISTOR, NATIONAL 2N5460 JFET, P-CHANNEL, TO-92 Q5SEMIC, TRANSISTOR, NATIONAL 2N5460 JFET, P-CHANNEL, TO-92 R1 RES, METALOXIDE YAGEO 5.6W-1 FILM, 1 W, 5.6 OHM, 5% R2 RES, METAL OXIDE YAGEO5.6W-1 FILM, 1 W, 5.6 OHM, 5% R3 RES, METAL FILM, YAGEO 33.2X RN55, ¼ W,33.2 OHM, 1% R4 RES, METAL FILM, YAGEO 33.2X RN55, ¼ W, 33.2 OHM, 1% R5RES, METAL FILM, YAGEO 60.4X RN55, ¼ W, 60.4 OHM, 1% R6 RES, METAL FILM,YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R7 RES, METAL FILM, YAGEO 499KX RN55,¼ W, 499 OHM 1% R8 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R9RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R10 RES, METAL FILM,YAGEO 499KX RN55, ¼ W, 499 OHM 1% R11 RES, METAL FILM, YAGEO 511X RN55,¼ W, 511 OHM, 1% R12 RES, METAL FILM, YAGEO 100X RN55, ¼ W, 100 OHM, 1%R13 RES, METAL FILM, YAGEO 100X RN55, ¼ W, 100 OHM, 1% R14 RES, METALFILM, YAGEO 100X RN55, ¼ W, 100 OHM, 1% R15 RES, METAL FILM, YAGEO1.00KX RN55, ¼ W, 1.00K, 1% R16 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W,10.0K, 1% R17 RES, METAL OXIDE YAGEO 5.6W-1 FILM, 1 W, 5.6 OHM, 5% R18RES, METAL OXIDE YAGEO 5.6W-1 FILM, 1 W, 5.6 OHM, 5% R19 RES, METALFILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R20 RES, METAL FILM, YAGEO10.0KX RN55, ¼ W, 10.0K, 1% R21 RES, METAL FILM, YAGEO 2.80KX RN55, ¼ W,2.80K, 1% R22 RES, METAL FILM, YAGEO 301KX RN55, ¼ W, 301K, 1% R23 RES,METAL FILM, YAGEO 2.0KX RN55, ¼ W, 2.0K, 1% R24 RES, METAL FILM, YAGEO100KX RN55, ¼ W, 100K, 1% R25 RES, METAL FILM, YAGEO 2.0KX RN55, ¼ W,2.0K, 1% R26 RES, METAL FILM, YAGEO 200X RN55, ¼ W, 200 OHM, 1% R27 RES,METAL FILM, YAGEO 100KX RN55, ¼ W, 100K, 1% R28 RES, METAL FILM, YAGEO10.0KX RN55, ¼ W, 10.0K, 1% R29 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W,10.0K, 1% R31 RES, METAL FILM, YAGEO 100X RN55, ¼ W, 100 OHM, 1% R32RES, METAL FILM, YAGEO 75X RN55, ¼ W, 75 OHM, 1% R33 RES, METAL FILM,YAGEO 51.1X RN55, ¼ W, 51.1 OHM, 1% R35 RES, METAL FILM, YAGEO 549XRN55, ¼ W, 549 OHM, 1% R36 RES, METAL FILM, YAGEO 20X RN55, ¼ W, 20 OHM,1% R37 RES, METAL FILM, YAGEO 15X RN55, ¼ W, 15 OHM, 1% R38 RES, METALFILM, YAGEO 2.80KX RN55, ¼ W, 2.80K, 1% R39 RES, METAL FILM, YAGEO2.80KX RN55, ¼ W, 2.80K, 1% R40 RES, METAL FILM, YAGEO 51.1KX RN55, ¼ W,51.1K, 1% R41 RES, METAL FILM, YAGEO 1.00KX RN55, ¼ W, 1.00K, 1% R42RES, METAL FILM, YAGEO 49.9KX RN55, ¼ W, 49.9K, 1% R43 RES, METAL FILM,YAGEO 100KX RN55, ¼ W, 100K, 1% R44 RES, METAL FILM, YAGEO 100KX RN55, ¼W, 100K, 1% R45 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R46RES, METAL FILM, YAGEO 100KX RN55, ¼ W, 100K, 1% R47 RES, METAL FILM,YAGEO 100KX RN55, ¼ W, 100K, 1% R48 RES, METAL FILM, YAGEO 200X RN55, ¼W, 200 OHM, 1% R49 RES, METAL FILM, YAGEO 2.0KX RN55, ¼ W, 2.0K, 1% R50RES, METAL FILM, YAGEO 2.0KX RN55, ¼ W, 2.0K, 1% R51 RES, METAL FILM,YAGEO 301KX RN55, ¼ W, 301K, 1% R52 RES, METAL FILM, YAGEO 2.80KX RN55,¼ W, 2.80K, 1% R53 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1%R54 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R55 RES, METALFILM, YAGEO 2.80KX RN55, ¼ W, 2.80K, 1% R56 RES, METAL FILM, YAGEO2.80KX RN55, ¼ W, 2.80K, 1% R57 RES, METAL FILM, YAGEO 51.1KX RN55, ¼ W,51.1K, 1% R58 RES, METAL FILM, YAGEO 1.00KX RN55, ¼ W, 1.00K, 1% R59RES, METAL FILM, YAGEO 49.9KX RN55, ¼ W, 49.9K, 1% R60 RES, METAL FILM,YAGEO 100KX RN55, ¼ W, 100K, 1% R61 RES, METAL FILM, YAGEO 100KX RN55, ¼W, 100K, 1% R62 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% R63RES, METAL FILM, YAGEO 100KX RN55, ¼ W, 100K, 1% R64 RES, METAL FILM,YAGEO 100KX RN55, ¼ W, 100K, 1% R65 RES, METAL FILM, YAGEO 200X RN55, ¼W, 200 OHM, 1% R66 RES, METAL FILM, YAGEO 2.0KX RN55, ¼ W, 2.0K, 1% R67RES, METAL FILM, YAGEO 2.0KX RN55, ¼ W, 2.0K, 1% R68 RES, METAL FILM,YAGEO 301KX RN55, ¼ W, 301K, 1% R69 RES, METAL FILM, YAGEO 2.80KX RN55,¼ W, 2.80K, 1% R70 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1%R71 RES, METAL FILM, YAGEO 10.0KX RN55, ¼ W, 10.0K, 1% T1 MISC, OTHER,SCHOTT 67125350 INDUCTOR, T1 CARRIER TRANSMIT T2 MISC, OTHER, SCHOTT67109510 INDUCTOR, 1.544 MHz T1 U1 IC, ANALOG, T1 PCM LEVEL ONE LXT312REPEATER/TRANS- CEIVER U2 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8U3 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U4 IC, OP AMP, HIGHNATIONAL LM318N SPEED, DIP8 U5 IC, OP AMP, HIGH NATIONAL LM318N SPEED,DIP8 U6 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U7 IC, ANALOG,LASER SHARP IR3C01 DIODE DRIVER, DIP8 U8 IC, OP AMP, HIGH NATIONALLM318N SPEED, DIP8 U9 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U10PIN PHOTODIODE, HEWLETT HP5082-4207 TO-18 PACKARD U11 IC, OP AMP, HIGHNATIONAL LM318N SPEED, DIP8 U12 IC, OP AMP, HIGH NATIONAL LM318N SPEED,DIP8 U13 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U14 IC, OP AMP,HIGH NATIONAL LM318N SPEED, DIP8 U15 IC, OP AMP, HIGH NATIONAL LM318NSPEED, DIP8 U16 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U17 PINPHOTODIODE, HEWLETT HP5082-4207 TO-18 PACKARD U18 IC, OP AMP, HIGHNATIONAL LM318N SPEED, DIP8 U19 IC, OP AMP, HIGH NATIONAL LM318N SPEED,DIP8 U20 IC, OP AMP, HIGH NATIONAL LM318N SPEED, DIP8 U21 IC, OP AMP,HIGH NATIONAL LM318N SPEED, DIP8 VR1 RES, TRIMPOT, ⅜ SQ., BOURNS3299W-105 ½ W, 1.0M, 10%, TOP ADJ, 25 TURN VR2 RES, TRIMPOT, ⅜ SQ.,BOURNS 3299W-104 ½ W, 100K, 10%, TOP ADJ, 25 TURN VR3 RES, TRIMPOT, ⅜SQ., BOURNS 3299W-501 ½ W, 500 OHM, 10%, TOP ADJ, 25 TURN VR4 RES,TRIMPOT, ⅜ SQ., BOURNS 3299W-503 ½ W, 50K, 10%, TOP ADJ, 25 TURN VR5RES, TRIMPOT, ⅜ SQ., BOURNS 3299W-105 ½ W, 1.0M, 10%, TOP ADJ, 25 TURNVR6 RES, TRIMPOT, ⅜ SQ., BOURNS 3299W-105 ½ W, 1.0M, 10%, TOP ADJ, 25TURN W1 CONN, HEADER SULLINS PZC36SAAN STICK, .025 SQ/.230 L POST, 1X36,GOLD W2 CONN, HEADER SULLINS PZC36SAAN STICK, .025 SQ/.230 L POST, 1X36,GOLD W3 CONN, HEADER SULLINS PZC36SAAN STICK, .025 SQ/.230 L POST, 1X36,GOLD W4 CONN, HEADER SULLINS PZC36SAAN STICK, .025 SQ/.230 L POST, 1X36,GOLD XI CRYSTAL, 6.176 MHz US CRYSTAL U49-18-6176SP (T1)

What is claimed is:
 1. An atmospheric turbulence resistant opticalcommunication system comprising: a transmitter that includes a waveformshaping modulator, an optical source, and beam forming optics forproducing a collimated optical beam, a receiver located in aline-of-sight path with said optical beam and including a plural numberof focusing receiving lenses of equal diameter spaced apart in a planenormal to said optical beam a distance greater than said receiving lensdiameter, a separate photodetector for each of said receiving lenses,and separate signal controlled gain amplifiers for each of saidphotodetectors, and an automatic gain control circuit coupled to receiveand combine inputs from all of said signal controlled gain amplifiersand conditioned to provide a combined output signal of constant level.2. An optical communication system according to claim 1 wherein saidreceiver is comprised of only a pair of receiving lenses,photodetectors, and signal controlled gain amplifiers.
 3. An opticalcommunication system according to claim 1 wherein said signal controlledgain amplifiers detect the signal-to-noise ratio from their respectivephotodetectors and said automatic gain control circuit provides saidcombined output with a contribution from each photodetector weighted inaccordance with the signal-to-noise ratio thereof.
 4. An opticalcommunication system according to claim 1 further comprising thresholddetection circuitry for each of said photodetectors to establish aminimum threshold for signals from each of said photodetectors.
 5. Anoptical communication system according to claim 1 wherein said opticalsource in said transmitter is a laser diode.
 6. An optical communicationsystem according to claim 1 wherein said photodetectors are allnoncoherent receivers.
 7. An optical communication system according toclaim 1 wherein said receiver further includes filters in front of saidreceiving lenses to reduce the effects of background radiation.
 8. Anoptical communication system according to claim 1 wherein said opticalsource is a laser diode and said beam forming optics in said transmitterinclude a collimating lens having a diameter of about one inch focusedon said laser diode, and each of said receiving lenses is about twoinches in diameter and is focused on said photodetector therefor.
 9. Anoptical communication system according to claim 8 wherein saidcollimating lens produces said collimated optical beam with anelliptical cross section, the major axis of which is verticallyoriented, and said receiving lenses are spaced from each other in ahorizontal direction.
 10. An optical communication system according toclaim 1 wherein said signal controlled gain amplifiers amplify outputsfrom their respective photodetectors with a gain that is proportional tothe signal-to-noise ratio thereof, so that said combined output signalis weighted greatest by the photodetector having the greatestsignal-to-noise ratio.
 11. An open-air optical communication system thatminimizes distortions due to atmospheric attenuation and scatteringcomprising: an optical transmitter that generates a collimated opticalbeam from a modulated light source, an optical receiver including aplurality of receiving lenses of equal diameter and focal lengths alllocated in optical communication with said optical transmitter and inthe path of said optical beam and separated from each in a directionperpendicular to said optical beam by a distance at least as great assaid receiving lens diameter, a separate optical photodetector producingan electronic output for each of said receiving lenses, a separatesignal controlled gain amplifier circuit coupled to each of said opticalphotodetectors for detecting the signal-to-noise ratio of saidelectronic output therefrom, and an automated gain control stage thatreceives inputs from all of said signal controlled gain amplifiercircuits and which produces a combined electronic output signal weightedin accordance with the signal-to-noise ratios of said signal controlledgain amplifier circuits.
 12. An optical communication system accordingto claim 11 further comprising a threshold detection circuit for each ofsaid photodetectors to ensure at least a minimum signal strength foreach of said signal controlled gain amplifier circuits in order toprovide an input therefrom to said automated gain control stage.
 13. Anoptical communication system according to claim 11 wherein said opticalreceiver is comprised of only a pair of receiving lenses, each about twoinches in diameter, and said optical transmitter employs a singletransmitting lens that has a diameter of about one inch.
 14. An opticalcommunication system according to claim 13 wherein said transmittinglens emits a collimated beam having an elliptical cross section with amajor axis oriented in a vertical direction and said receiving lensesare spaced from each other in a horizontal direction.
 15. In an open-airoptical communication system employing a transmitter that generates acollimated optical beam modulated by a communication signal and areceiver disposed in optical communication with said collimated opticalsignal beam to detect and demodulate said collimated optical beam toextract said communication signal therefrom, the improvement whereinsaid receiver is comprised of a plurality of receiving lenses of equaldiameter that all lie in said optical path of said collimated opticalbeam and which are separated from each other in a plane normal to saidoptical path by a distance at least as great as said receiving lensdiameter, a separate photodetector for each of said receiving lenses toindependently detect said collimated optical beam therethrough, separategain amplifiers for each of said photodetectors, and a common automaticgain-controlled circuit coupled to receive inputs from all of saidseparate gain amplifiers and to combine said inputs to produce a singledemodulated output communication signal having a constant level.
 16. Anoptical communication signal according to claim 15 wherein saidtransmitter includes a single laser diode and a single transmitting lensfocused on said laser diode, and said receiver includes only a pair ofsaid receiving lenses, each focused on a separate noncoherent receiverphotodetector.
 17. An optical communication system according to claim 16wherein said single transmitting lens and said collimated beam has anelliptical cross section with a vertically oriented major axis and saidpair of receiver lenses are spaced horizontally from each other.